A conventional image-reader known in the art is provided with two image-reading sensors disposed on a path along which a document sheet is conveyed. One image-reading sensor is provided for the front surface of the document sheet, and the other for the back surface of the document sheet, whereby the two image-reading sensors can simultaneously read both surfaces of a document sheet conveyed along the conveying path.
Japanese patent application publication No. H8-265576 describes an information processor having two image-reading sensors corresponding to both surfaces of a document sheet, and a single signal processing circuit. One image-reading sensor is provided for the front surface of the document sheet, and the other is provided for the back surface of the document sheet. Each of two image-reading sensors reads the document sheet in units of lines along a main scanning direction. Based on the parameters individually set for the two image-reading sensors, the signal processing circuit performs image processes on image signals received from the image-reading sensors, while alternating between the two image signals.